Induction heating



June 27, 1944. E. J. LIMPEL INDUCTION HEATING Filed July 31, 1942 INVENTOR. 56AM AT TORNEY Patent'e'd June 27, 1944 UNITED STATES PATENT OFFICE v INDUCTION HEATING Eugene J. Llmpel, Milwaukee, Wis assignor to A. 0. Smith Corporation, Milwaukee, Win, a corporation of New York Application July 31, 1942, Serial No. 453,004

This invention relates to the induction heat- Where the opening in the end of a heavy walled large diameter nose of a bomb casing is only about two inches in diameter there is diillculty in getting enough flux to pass through the opening to effect a satisfactory heating of the metal immediately at and adjacent the edge of the opening. This difficulty arose from the apparent impossibility of extending a sumcient core structure through so small a hole. It was thought for a long time by those connected with the development that the difficulty encountered would make induction heating inapplicable to the bomb casing after it had reached the 'specifled stage of forming.

The invention has as its principal object the teasing of a greater proportion of flux into and through the relatively small hole at the end of the partially formed nose on theblank and to thereby obtain a, heating of the metal adjacent the hole more nearly equal to that of the main body of the nose.

According to the invention in its preferred embodiment a small removable core plugis applied to the opening in each bomb casing prior to the insertion of the latter into the induction furnace, the plug being of sufficient length to co-operate with an inner and outer core structure of the furnace and substantially complete a continuous magnetic circuit through the relatively small opening in the bomb casing.

The invention is illustrated in the accompanying drawing in which: Y

Figure 1 is a vertical central section -through the nose of a bomb casing showing a core plug in position for drop ing into the hole in the casing;

Fig. .2 is a vertical central section through an induction furnace showing the bomb casing with its core plug in position for aheating operation;

Fig.3 is a transverse section through the furnace taken on line 3-3 of Fig. 2;

Fig. 4 is a top plan view of a laminated plug;

and a Fig. 5 is a similar, view of a modified construction of plug.

Referring to the drawing the bomb casing I to be heated has its upper end partially formed as a nose 2 with only a small hole. 3 at the end..

Acore plug 4 having a diameter smaller than that of hole 3 and a flanged upper end I is droppedinto the hole I, the flange I on the plug serving to support the plug on the bomb casing. The plug 4 is laminated as shown in Fig. 4 or else radially slotted around its circumference as shown in Fig. 5- to prevent excessive eddy currents therein.

After applying the plug 4 to the bomb casin the latter is conveyed to a position beneath the induction furnace and then raised vertically into the furnace as indicated by the arrow in Fig. 2 of the drawing.

The furnace is a low cycle induction furnace having an outside core structure 6 suspended from an overhead support I. The core structure A central vertical core leg II, which is also I laminated, is raised upwardly inside the bomb casing and engages the lower end of plug as the latter enters the furnace. In alignment with the-leg II, a laminated vertically movable central pole piece I! fills the hole 8 in the upper core structure.

'The pole piece I! has a flange I3 which prevents it from dropping through the core 6 and which allows the pole piece to be raised when the plug 4 engages it from beneath as the bomb casing is raised to heating position.

The slight vertical movement of pole piece I: when raised by plug 4 and core leg ll enables the making of a continuous flux path through these parts and avoids shock on the frame of the core. Another way of avoiding such shock might be to provide a fixed pole piece for core 8 at the top and a cushion support for the inner leg ll so that when it hits plug 4 it retracts into its support.

The energizing coils H of the furnace are disposed to encircle the bomb casing in the region of its larger diameter. One or more auxiliary energizing coils II of smaller-diameter are disposed around and adjacent the tip of the Bomb uniformly in the time allotted for heating and the metal of the bomb casing at the edge of the opening 1 is heated practically as rapidly as therest of the nose. The current employedyis 1 low cycle, preferably about cycles per second.

Upon completion of the heating of the bomb casing the core leg II and bomb casing l are lowered from the furnace and the bomb casing is conveyed to an adjacent forging machine where the forming of the nose is completed. The plug 4 is removed by an operator with a pair of tongs before forging the bomb casing. The plug 4 may be used again in another bomb after the plug cools. A supply of plugs is kept on hand for successive heating Operations.

Various embodiments of the invention may be employed within the scope of 'the accompanying claims.

The invention is claimed as follows:

1. In an induction furnace for heating a partially closed nose of a tube, a core structure providing a substantially closed flux path adapted to pass longitudinally through the tube with a gap in the structure at the aperture in the tip of the nose, and a temporary core member adapted to be inserted in the aperture to bridge the gap in the core structure of the furnace.

2. In an induction furnace for heating a partially closed nose of a tube, a core structure providing a substantially closed flux path adapted to pass longitudinally through the tube with a gap in the structure at the aperture in the tip of the nose, and a temporary core member adapted to be inserted in the aperture to bridge the gap in the core structure of the furnace,.said memher being adapted to be carried by the tube being heated and adapted to be removed for cooling and repeated use upon removal of the tube from the furnace,

3. In an induction furnace for heating a partially closed nose of a tube, a core structure providing a substantially closed ilux path adapted to pass longitudinally through the tube with a gap in the structure at the aperture inthe tip of the nose, a temporary core member adapted to be inserted in the aperture to bridge the gap in the core structure of the furnace, energizing coils adapted to encircle the tube for the core structure of the furnace, and an auxiliary energizing coil adapted to be .positioned irnmediately adiacent the nose tip of the tube and encircling the temporary core member to saturate the same with flux.

4. An induction furnace for heating the partially formed nose of a bomb casing having a small aperture at the tip, comprising an outer core structure having a substantially closed top and an o'pen bottom for receiving the upper nose end of the bomb casing, means to raise a bomb easing into the furnace to a position where the tip of the nose is adjacent the central portion of the core structure, a central vertically disposed core structure for co-operation with said outer core structure to provide a substantially closed magnetic flux circuit, means to raise said central core structure inside the bomb casing until its upper end is adjacent the inside of the tip of the nose of the latter, means to produce a magnetic flux in said core structure, and a core plug passing through the aperture in the tip of the partially formed nose and bridging the gap between the central portion of said outer core structure iand the upper end'of said central core strucure. 1

5. An induction furnace for heating the partially formed nose of a bomb casing having a small aperture at the tip, comprising .an outer core structure having a substan ially Clo-W1 and an open bottom for receiving the upper nose end of the bomb'casing, means to raise a bomb casing into the furnace to a position where the tip of the nose is adjacent the central portion of the core structure, a central vertically disposed core structure for co-operation with said outer core structure to provide a substantially closed magnetic flux circuit, means to raise said central corestructurefinside the bomb casing until its upper end is adjacent the inside of the tip of the nose of the latter, means to produce a magnetic flux in said core structure, and separate means including an additional core member to concentrate flux in the aperture in the tip of the nose of the bomb casing.

6. An induction furnace for heating the partially formed nose of a bomb casing having a small aperture at the tip, comprising an outer core structure having an open bottom for receiving the upper nose and of a bomb casing, the

outer core structure having its top substantially closed and provided with a central pole piece which is vertically movable through an opening therein, an individual core plug disposed in the aperture in the tip of the nose of said bomb casing to be heated and carried by said casing, means to raise the bomb easing into the furnace to a position where the plug strikes said movable pole piece,'an inner vertically disposed core structure for co-operation with said outer core structure to provide a substantially closed magnetic flux circuit, means to raise said inner core structure inside the bomb casing until its upper end engages the lower end of said core plug, and means to produce a magnetic flux in said core striicture.

7. An induction furnace for heating the partially formed nose of a bomb casing having a small aperture at the tip, comprising an outer core structure having an open bottom for receivinglthe upper nose end of a bomb casing, the outer core structure having its top substantially closed and provided with a central pole piece, an

0 individual core plug disposed in the aperture in the tip of the nose of said bomb casing to be heated and carried by said casing, means to raise the bomb casing into the furnace to a position where the plug strikes said movable pole piece, an inner vertically disposed core stnicture for co-operation with said outer core structure to provide a substantially closed magnetic flux circuit, means to raise said innercore structure inside the bomb casing until its upper end engages the lower end of said core plug, energizing coils encircling the bomb casing in the lower end of the furnace,

and an auxiliary energizing coil adjacent the tip of the bomb casing and encircling said individual coreplug to concentrate flux therein.-

8. In an induction furnace having relatively movable core members adapted to receive an article to be-heated between them with a gap in the flux path axially of a relatively small aperture in the article, a temporary core element adapted to be carried by the article and disposed in the aperture therein to bridge the gap during the heating cycle, said core members moving relatively into engagement with said element to provide for the transference of flux therebetween during operation of the furnace.

EUGENE J. LIMPEL. 

